The materials used in automotive engine blocks and in automotive pistons have always had to accommodate wear between the rapidly moving pistons and the cylinder bores in which they reciprocate. Cast iron engine blocks and cast iron pistons are very durable and wear resistant, but they have the disadvantage of excessive weight. Both aluminum pistons and aluminum engine blocks have been used in automotive engines, but some provision must be made to reduce scuffing and wear due to the motion between the piston and its mating cylinder wall.
Iron cylinder liners have been used in cast aluminum engine blocks. However, both the engine block and the cylinder liner must be carefully machined so that they fit together. It is also known to cast the aluminum block around a preformed iron liner, but this complicates the casting process. It is also known to cast the entire aluminum block out of a hypereutectic aluminum-silicon alloy such as 390 aluminum alloy. Such a material is extremely wear resistant, but it is a composition which is difficult to machine and hard to cast. Accordingly, it is preferred not to cast the entire engine block out of the 390 alloy. It has also been practiced to cast the bulk of the aluminum engine block out of a lower silicon content aluminum alloy such as 319 aluminum alloy and then use either iron liners or make provision for a high silicon content aluminum alloy liner. All of these practices have the disadvantage of requiring two different materials in the formation of the engine block and requiring additional expense to insert the cylinder liner material in a suitable fit in the engine block.
Accordingly, it is an object of the present invention to provide an improved method of forming a scuff- and wear-resistant liner in a relatively low silicon content aluminum alloy cast engine block. The new lining material and practice is less expensive to form and provides unexpectedly good wear properties.
It is a further object of our invention to provide a practice for forming a thermal sprayed coating on a low silicon aluminum alloy cast engine block that offers the wear-resistance properties of an iron liner or a high silicon content liner without the attendant costs of forming these structures in the cast block.
It is a still further object of our invention to provide an alternative solution to the scuff problem by providing a thermally-sprayed, wear-resistant coating on a complementary surface such as the skirt of an aluminum piston intended to operate within a high silicon cast aluminum alloy engine block or cylinder bore.
In accordance with a preferred embodiment of our invention, these and other objects of our invention are accomplished as follows.